My '70 300 has the four port red plastic vacuum operated water valve. I understand that the theory of operation is that it's controlled by vacuum. Varying the amount of vacuum with the slide control changes the valve from closed at "cool" to open at "hot".
When mine is all the way at cool, i still feel warm water in the hoses on the heater core side of the valve. The engine side is hot. I think the valve may be leaking. I would expect the heater side to be cold.
Can the valve be...
Heat water valve questions
